1. Field of the Invention
The invention relates to manhole enclosures and systems for monitoring environmental parameters in subterranean enclosures. Specifically, the invention relates to a manhole cover with a signal transmitter for wireless monitoring of subterranean enclosures.
2. Description of the Background of the Invention
Wireless transmission of environmental parameters from manhole enclosures presents a number of challenges. The only way for a data signal relating to water depth, flow or temperature, for example, to be communicated wirelessly to the exterior is through a manhole cover; and manhole covers are typically made of metal. If they reach the surface, the radio signals are often too weak to coherently reach their destination. Various devices and methods have been proposed to address the problem.
One such device includes use of an antenna embedded in the road. Generally, an antenna is located on the surface next to the manhole entrance. The antenna may be mounted directly to the road's surface or in a trench to reduce the profile of the antenna on the surface. The antenna is connected to a radio transceiver inside the manhole by way of a coaxial cable. Connecting the underground transceiver to the above ground antenna, however, involves labor and equipment to prepare the surface, install conduit, and wire the components.
Some have tried mounting the antenna directly on the top side of the manhole cover. Like the road-embedded antenna, however, it is difficult to conceal the profile of the antenna because the antenna is mounted on top of the cover. This is particularly troublesome when plowing the road of snow. Another problem deals simply with the mass of the manhole cover; its metallic construction makes it difficult to remove and handle because of its weight. This results in damage to the equipment that may be located underneath the cover when the cover is removed from the manhole.
Another proposed design uses the metal cover itself as the antenna. A slot is machined in the manhole cover, which defines a slot antenna. Besides being self-contained, one advantage of the slot antenna cover is that because there is no antenna attached to the surface, the cover maintains its essentially plan profile. This design, however, does not address the problems associated with the heavy weight of the cover or water, dirt and debris clogging the slot and thus ruining transmission. Additionally, machining the slot antenna and connecting it to the transceiver adds to the cost of this device and cover.
Accordingly, there remains a need for an improved manhole cover with a signal transmitter for wireless monitoring of a subterranean enclosure. The present invention is directed toward meeting this need.